Parashath Bereshith, Laws of Ziziyoth, Page 6
6. The berachah over both the tallith gadhol and the tallith qatan should be recited whilst standing.
The custom of our teacher, the Ari z'l, was to wrap his head in the tallith qatan first, and only after that to put it on as he usually wore it. For that reason, he used to recite the berachah 'lehithattef' over the tallith qatan as well as over the tallith gadhol. This is a good custom to follow but, if one does not wrap one's head in the tallith qatan as the Ari z'l did, one should recite the berachah 'al mizwath zizith, ' and not 'lehithattef bezizith.'
This learning should be in memory of Maran, HaRav HaGaon Ovadia Yosef, ztz'l.